1. Field of the Invention
The present invention relates to a central mechanism in a tire vulcanizing press. More particularly, it is concerned with a central mechanism in a tire vulcanizing press including a latch mechanism for preventing a shaping bladder lower clamp supporting member from being brought down due to a downward internal pressure induced by a hot pressure medium (internal pressure) which is supplied into the bladder during vulcanization of a tire, and also including a heat retaining and insulating device.
2. Discussion of the Background
As well known, a central mechanism in a tire vulcanizing press is provided with means for holding and operating a bladder extensibly and contractibly, the bladder being capable of contacting an inner surface of a green tire, and means for supplying a hot pressure medium (e.g. steam) as an internal pressure medium for a vulcanizing press. According to a principal construction thereof, although there are various types, a lower clamp for the bladder is supported by a hydraulic cylinder and an upper clamp for the bladder is supported by a piston rod of another hydraulic cylinder, the latter cylinder being made movable vertically by a drive means (e.q. a hydraulic cylinder) provided separately, whereby the upper and lower clamps can be vertically moved simultanoeously or separately, thereby permitting operations required of the bladder such as close contact with the inner surface of the green tire, drawing out and extension of the bladder. For supplying a hot pressure medium such as steam into the bladder, a hot pressure medium supply pipe is connected from the interior or exterior of the hydraulic cylinder to a lower clamp supporting structure in the hydraulic cylinder.
During vulcanizing pressing of a green tire, as already known, upper and lower dies are closed and a bladder whose upper and lower clamp portions are supported by a central mechanism and which is in close contact with an inner surface of a tire sealed into the dies, under supply of a hot pressure medium. In this state, an internal pressure induced by the hot pressure medium acts vertically on the upper and lower clamp portions on the central mechanism side positioned at the die center, and the upper and lower clamp portions bear this internal pressure by being supported by the upper and lower dies. In a so-called post-in-well type vulcanizing press in which a shaping bladder housing well is provided in a surrounding and concentric relation to the central mechanism and the bladder is drawn into the well in a folded state, the lower clamp support portion moves below the lower die, so the above-noted downward internal pressure cannot be supported by the lower die and therefore it becomes necessary that a post member on the central mechanism side which supports the lower clamp portion be retained by another means. As this retaining means there is used, for example, a retaining pin which is inserted from the outside of the central mechanism, or a retaining spacer which is inserted similarly, or a latch mechanism capable of being opened and closed which is provided in the central mechanism and which is opened or closed to retain the post member, as will be described later.
A prior art central mechanism using a latch mechanism will now be described. What is illustrated in FIGS. 7, 8 and 9 is the central mechanism disclosed in Japanese Utility Model Laid-Open Publication No. 61997/83 filed by the applicant in the present case. The basic structure and latch mechanism in the said central mechanism are as follows.
A lower die 14 is fixedly mounted on a vulcanizer base 11 through a heat insulator 12 and a hot platen 13, (such being illustrated only partially because all of them are well known) and an upper die of a known structure (not shown) is disposed for opening and closing motions relative to the lower die 14. A green tire is indicated at 15 and an extensible and contractible bladder formed of rubber or any other suitable elastic material is indicated at 16. A housing well 2 of the central mechanism is vertically movably provided through a guide post 17 fixed in a central position of the lower die 14 and also through a lift means such as a knockout cylinder known in conventional tire vulcanizers and a link mechanism which connects a piston rod of said cylinder with the housing well 2. A lower bead ring 29 for supporting a lower bead portion of the green tire 15 is fitted on the outer periphery of an upper end of the housing well 2.
A support post 4 having at an upper end thereof a clamp ring hub 18 provided with a lower clamp 1 for the bladder 16 is provided through a central position of the housing well 2, namely, the press center, vertically movably through its slidable engagement with the inner surface of the well 2. Further, a center post 19 provided at an upper end with an upper clamp 5 for the bladder 16 is inserted centrally through the support post 4 vertically movably along the center bore of the support post 4 as a guide. To the clamp ring hub 18 is connected an inlet pipe 20 for steam or any other suitable hot pressure medium, which pressure medium can be supplied into the bladder 16 through a through hole 21. A hot pressure medium outlet passage 23 which communicates with the interior of the bladder 16 through a through hole 22 in the upper clamp 5 is formed through the center of the center post 19. A seal member between the center post 19 and the clamp ring hub 18 is indicated at 24, and a port 25 of the outlet passage 23 projects outwards from a notch 26 of the support post 4. Hydraulic cylinders are used as lift means for the posts 4 and 19 and, as illustrated in the drawing, a hydraulic lift cylinder 3 for the support post 4 and a like cylinder 6 for the center post 19 are both disposed below a partition wall 2a provided in an intermediate position of the housing well 2 in spaced relation to the posts 4 and 19 and in a built-in fashion. A piston rod 3a of the hydraulic lift cylinder 3 is connected through a connecting rod 27 to the clamp ring hub 18 side which is integral with the support post 4. On the other hand, a piston rod 6a of the hydraulic lift cylinder 6 is connected to a lower end of the center post 19 through a connecting portion 28. Since the lower clamp 1 of the bladder 16 and the lower bead ring 29 of the green tire 15 are separated, the bladder 16 can be drawn into the housing well 2 together with the upper and lower clamps 5 and 1 as will be described later. Therefore, a support mechanism using a latch 10 is provided for supporting the descent of the lower clamp 1 side caused by internal pressure during vulcanizing pressing for the green tire 15 under heating and pressure. More particularly, utilizing the partition wall 2a in the well 2, a pair of pin shafts 30 are opposedly provided rotatably and a pair of pinions 31, which are in mesh with each other, are mounted on the pin shafts 30. Further, a pair of latches 10 are attached to upper ends of the pin shafts 30 to hold therebetween a notched peripheral portion 4a of the support post 4. To one pin shaft 30 is connected an actuating link 33 which is driven by a piston rod 32a of a driving cylinder 32, whereby both latches 10 can be opened and closed to lock and unlock the support post 4. Further, a swivel-stop key 35 fixed to a bracket 34 provided by utilization of the partition wall 2a is engaged with the support post 4 only vartically movably through a notch 4b.
Such conventional central mechanism involves the following problems. As already known, the central mechanism itself is an assembled set, which is completed outside the vulcanizer in advance and then mounted to the base frame of the press in a central position of the lower die. In the foregoing mechanism in which pins or spacers are moved in and out, or the latch mechanism shown in FIGS. 5, 6 and 7 which comprises a pair of latches 10, driving cylinder 32 and actuating link 33, it is required to reassemble the mechanism after assembly and it is impossible to make assembly and adjustment from outside the vulcanizing press; besides, there are such disadvantages as an increase in the area occupied by the mechanism and the impossibility of obtaining a large effective stroke. The latch mechanism is superior to the pin or spacer in-out system, but the shape and size of the cylinder and link are extremely restricted because the driving cylinder 32 and the actuating link 33 are disposed planarly within the limited space in the well 2 and the latches 10 are opened and closed by a rotational motion. Moreover, only a short effective stroke is allowed for the piston rod of the cylinder and the moving radius of the link 33 becomes short, such that it is impossible to impart an exact and stable opening/closing motion to the latches 10. Further, since the hot pressure medium supply line as well as the center post and support post are disposed through the central mechanism, an effective utilization area is extremely restricted, thus imposing a great restriction on the design and assembly of the entire latch mechanism, and it is actually difficult to assemble and adjust of the mechanism.
Further, there arises heat propagation especially on the side of the upper portion of the central mechanism due to a thermal environment created by the hot pressure medium supplied into the bladder, heating means in the upper and lower dies and the hot pressure medium supplied into a dome which surrounds the upper and lower dies. In a convention construction in which the lower clamp side of the bladder is directly connected to a hydraulic cylinder, an undesirable influence is exerted on the cylinder side due to heating and such construction makes it difficult to adopt a heat progagation cut-off structure. Thus, hydraulic sealing and maintenance are extremely difficult, causing various difficulties. There are two types, in one of which the hydraulic cylinder as a main body of the central mechanism is provided at the center of the lower die vertically movably through a guide post, while in the other type the housing well as a main body of the central mechanism is provided in the guide post and the hydraulic cylinder is mounted in the well vertically movably. In both types, the hydraulic cylinders are required to be considerably long, thus leading to an increase in size of the central mechanism itself.
Moreover, it is difficult to effect heat insulation for the connection between the center post for vertical movement of the bladder upper clamp and the actuator as a drive source for the center post, and no consideration is given regarding the heat retention and insulation. Consequently, heat dissipation to the exterior and heat loss are large, and the temperature of the bladder lower portion and that of the lower bead ring portion become lower as compared with the respective upper portions, resulting in vulcanization of the portion concerned (lower portion of the tire) being apt to be delayed.